The waterborne coatings and ink industries require surfactants that provide excellent surface tension reducing capabilities for substrate wetting. Equilibrium surface tension performance is important when the system is at rest. End-users also need surfactants with good dynamic performance which is a measure of a surfactant's ability to provide wetting under high speed application such as when coatings are spray applied or inks are printed.
Traditional nonionic surfactants such as alkylaryl or alcohol ethoxylates, and ethylene oxide (EO)-propylene oxide (PO) copolymers have excellent equilibrium surface tension performance but are generally characterized as having poor dynamic surface tension reduction. In contrast, certain anionic surfactants such as sodium dialkyl sulfosuccinates can provide good dynamic results, but these are very foamy and impart water sensitivity to the finished coating.
Surfactants based on acetylenic glycols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol and its ethoxylates are known for their good balance of equilibrium and dynamic surface tension reducing capabilities with little of the negative features of traditional nonionic and anionic surfactants. The molecules, however, may not provide the very low surface tension reduction needed for the wetting of contaminated surfaces or low surface energy substrates. In those cases, end-users may require silicone or fluorocarbon based surfactants which may be costly, foamy, exhibit poor dynamic performance and often cause adhesion problems.
The following patents and articles describe various acetylenic alcohols and their ethoxylates as surface active agents:
U.S. Pat. No. 3,268,593 discloses ethyleneoxide adducts of tertiary acetylenic alcohols represented by the structural formula ##STR2## wherein R.sub.1 and R.sub.4 are alkyl radicals having from 3-10 carbon atoms and R.sub.2 and R.sub.3 are methyl or ethyl and x and y have a sum in the range of 3 to 60, inclusive. Specific ethyleneoxide adducts include the ethyleneoxide adducts of 3-methyl-1-nonyn-3-ol; 7,10-dimethyl-8-hexadecyne-7,10-diol; 2,4,7,9-tetramethyl-5-decyne-4,7-diol; and 4,7-dimethyl-5-decyne-4,7-diol. Preferably, the ethyleneoxide adducts range from 3 to 20 units. The patentees point out that these ethyleneoxide adducts have outstanding wetting property and that the presence of the acetylenic bond in the hydrophobic chain increases water solubility and improves surfactant properties. As the oxyethylene chain link increases, both detergency and amount of foam increase, and the wetting times decrease with increasing polyoxyethylene chain length.
U.S. Pat. No. 4,117,249 discloses acetylenic glycols represented by the structural formula ##STR3## wherein R is hydrogen or an alkenyl radical. The acetylenic glycols are acknowledged as having utility as surface active agents and they can be used as wetting agents, dispersants, antifoaming nonionic agents and viscosity stabilizers.
In an article, Schwartz, The Importance of Low Dynamic Surface Tension in Waterborne Coatings, Journal of Coatings Technology (1992), there is discussion of surface tension properties in waterborne coatings and a discussion of dynamic surface tension in such coatings. Equilibrium surface and dynamic surface tension are evaluated for several surface active agents including the ethyleneoxide adducts of acetylenic glycol, e.g., the 4,7-ethyleneoxide the 3.5 mole adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol where the number of ethyleneoxide units ranges from about 1.3 to 30, as well as the acetylenic glycols themselves, and ethyleneoxide adducts of other aromatic and aliphatic alcohols, e.g., nonylphenol and lauryl alcohol. At a concentration of 0.1% in distilled water, the dynamic surface tension ranges from a low of about 32 to a high of 72 dynes per centimeter.